What You Need

In class this week, you will review how to grab data from the Earth Explorer website. The Earth Explorer website is a data portal run by the USGS. Here you can find many different types of remote sensing and other data for both the US and in some cases, the globe.

IMPORTANT: Be sure to order your data several days ahead of time or else you won’t have it in time to finish your homework.

How to Download Landsat Remote Sensing Data from Earth Explorer

Step 1: Define Your Study Area (AOI)

When searching for data, the first thing that you need to do is to define your area of interest (AOI). Your AOI for this week, is defined by the boundary of the Cold Springs fire extent. You could type in the x,y vertices of each corner of the boundary, but if you have an Earth Explorer account, you can upload a ZIPPED up shapefile that contains the boundary instead.

Remember that the spatial extent of a spatial object, is the geographic area that your data cover on the ground. In the case of vector data - this represents the minimum and maximum x and y values for each corner boundary of the dataset. Source: Colin Williams, NEON.

Important: Be sure to use a square / rectangular extent polygon. If you have too many vertices in your extent polygon, the website won’t accept it as an extent file.

To define your AOI in Earth Explorer:

Zip up extent file that you want to use. Be sure to use a square extent, if you have too many vertices it won’t work. Lucky for us there is a zip file already zipped up and ready to go in your cold-springs-fire download! data/cold-springs-fire/vector_layers/fire_boundary_box_shp.zip

Be sure to create an account. You will need it to be able to use your shapefile extent to search for data. Now, it’s time to search for data.

In the search criteria, click on shapefile tab. Select the zip file above as the shapefile that represents the SPATIAL EXTENT of your study area - the Cold Springs fire site.

At the bottom of the search criteria window, select a range of dates. A month before and after the fire is a nice starting point.

Notice the shapefile tab mid way down in this image. This is the tab you need to click on to upload a zipped up shapefile extent to Earth Explorer. At the bottom of the image, notice there is a date range tab. This is where you set the data collection date range that you require. In your case you want all images collected around the Cold Springs fire which occurred July 10-14 2016.

Step 2: Define the Data That You Want to Download

Next click on the Data sets tab. Notice that there are a lot of different data available from Earth Explorer! You are interested in Landsat - specifically Landsat 8. You can find Landsat in the Landsat archive drop down. Expand that drop down to find:

Landsat - Landsat Collection 1 Level-2 (On-Demand)

The Landsat 8 data are located in the Pre-Collection drop down. Be sure to select Landsat 8 OLI/TIRS C1 Level-2.

Step 3: Define Selection Criteria

Next select the Additional Criteria tab. Here is where you can limit results by % cloud cover. Start with Less than 20% cloud cover and see what you get as data results.

When you click on the additional criteria tab, you can further filter data results. In this case, low cloud cover is a priority for your analysis. You can select Less than 20% cloud cover as a starting place to see if you can find a scene with little to not cloud cover over your AOI (area of interest).

Step 4: View Results & Select Data to Order / Download

Finally click on the Results tab. Here you see all of the scenes available for “order” from the website that cover your study area.

Notice that you can click on the icons below the scene to see the scene itself rendered on the map and to see the footprint (or extent) of the scene relative to your study area.

Pick a scene that is:

closest to the pre-fire date (July 10 2016) and also that has the least amount of cloud cover close to your study area.

Step 5: Order Your Data

Click the shopping cart icon to add the data to your cart.

Click on “item basket” in the upper right hand corner of your browser to see what you have ordered.

Click on Proceed to Checkout

Then finally, click on Submit Order

IMPORTANT: It will take a few days for the link that you can use to download your data to be emailed to your account. Order now!

Explore Newly Downloaded Data

In this case, you wanted to download a scene very close to Julian day 189. Notice that the spatial extent of the data that you download from Earth Explorer is much broader than the data that you worked with for your homework last week. The extents are different because your instructor cropped the class data to make is easier to work with!